The present invention pertains generally to explosives and in particular to energetic casings for warheads.
Aluminum and alloys thereof have been used extensively in explosives as a powder metal fuel for detonation. It has been disclosed in U.S. Pat. No. 3,000,308 that aluminum can contribute to the energy of an explosive without being in a powder, e.g., ribbon, foil, or strip. Thus, if aluminum is added to an explosive composition in a nonpowder form as a reinforcement aid, the energy contents of the composition is not significantly reduced.
The use of aluminum or aluminum alloys in the manufacture of warhead casing has been limited. In U.S. Pat. No. 2,998,772 it was disclosed that PBX explosives do not need a strong casing and thus a thin sheet aluminum could be used as the casing. Nothing was disclosed in regard to the use of aluminum in a casing requiring mechanical strength or about the possible contribution of aluminum or its alloys to the air-blast energy. In G.B. Patent No. 1,018,089 it was disclosed that aluminum was not suited for the production of casings for blasting cartridges because aluminum produces large spinters upon detonation. Iron which had been pressed and sintered was taught to be the best casing material, even though the mechanical strength and imperviousness to fluid were considered to be poor.
The large contribution that aluminum can make to an airblast was first realized in U.S. patent application No. 494,957. The patent application taught broadly that the controlling factors were a large percentage of aluminum in the warhead casing and the porosity in the warhead casing. The manner of fabricating the warhead casing was considered to be unimportant and that no alloy had particular advantage over aluminum or other alloys. Although the tested warhead casing made from commercially available pressed aluminum foam showed a large increase in the air-blast efficiency, the warhead casings would only have a very limited use because of the poor mechanical strength, its absorption of water, high cost of manufacture arising from the complexity and length of processing.